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<h2><b>hcurl</b></h2><p> 

<code>hcurl(<i>uexpr,vexpr</i>)</code><p> 

Calculates the vertical component of the curl (ie, vorticity) at each grid
point using finite differencing on the grids provided. It is assumed that
<code><i>uexpr</i></code> gives the U Wind component, and that
<code><i>vexpr</i></code> provides the V Wind component.<p> 

<h3>Usage Notes</h3><p> 

<ol>
<li>The alghorithm used for the finite difference calculation is described
as an Example for the <a href="gradfunccdiff.html"><code>cdiff</code></a>
function.<p> 

<li>The function assumes an X-Y varying dimension environment, and will
not operate unless that is the case. The <a
href="gradcomddefine.html"><code>define</code></a> command can
be used in conjunction with the <code>hcurl</code> function to create 3 or
4 dimensional fields of vorticity, from which
vertical cross-sections could be displayed. <p>

<li>The boundaries of the grid are set to missing. <p>

<li>The radius of the earth used in the calculation is in meters; thus the
units of the wind expressions provided would normally be m/s. <p>
</ol>
<h3>Examples </h3><p>

<ol>
<li>To display the vorticity: <p>

<dd><code>d hcurl(u,v) </code><p>

<li>If you want to display a vertical cross section of vorticity, you
first need to calculate it over a 3-Dimensional region: <p>

<dd><code>set lon 0 360 
<dd>set lat -90 90 
<dd>set lev 1000 100 
<dd>define vort = hcurl(u,v) 
<dd>set lon -90 
<dd>display vort </code>
</ol>

